The present invention relates to an apparatus and a method for disinfecting water with on-site production of oxidizing/disinfectant products.
The generic term “water” is used to reference water to be disinfected, such as civil and industrial wastewater, cooling water of rivers, lakes or seas, potable waters and process water in general.
Water disinfection is necessary in order to prevent the proliferation of organisms, such as pathogen and environmental bacteria, fungi, algae, which can cause hygienic and sanitary problems or problems in terms of lack of efficiency of systems.
At least three different chemical reactions for obtaining disinfectant/oxidizing chemical products for water disinfection from reagents are known:
a transformation reaction of sodium chlorite and hydrochloric acid into chlorine dioxide, sodium chloride and water;
a transformation reaction of sodium chlorite in the presence of sulphuric acid to yield chlorine dioxide, sodium chloride, sodium sulphate and water;
and finally a transformation reaction of sodium chlorate, sodium chloride and sulphuric acid into chlorine dioxide, chlorine, sodium sulphate and water.
Methods and apparatuses for producing chlorine dioxide are known.
For example, U.S. Pat. No. 4,534,952 discloses the on-site generation of chlorine dioxide in a confined reaction region filled with the reagents necessary for its generation. Such reaction region is at a pressure that is sufficient to prevent the chlorine dioxide from forming a continuous gaseous phase, with the consequence of its possible explosion.
The method disclosed in U.S. Pat. No. 4,534,952 has the drawback that it is necessary to always maintain a pressure in the reaction medium in order to avoid the risk of explosions caused by the passage of the chlorine dioxide to the gaseous phase.
US-A-2003/0138371 (McWhorther et al.) discloses a method and an apparatus for generating gaseous mixes of chlorine dioxide and chlorine produced by reacting an inorganic acid with an aqueous solution of an alkaline metal chlorate by controlled introduction of the inorganic acid in the aqueous solution of the alkaline metal chlorate. The disinfectant product, together with steam, is formed in a head space of a reactor, from which it is removed and dissolved in water to obtain a product stream.
US-A-2003/0138371 discloses a method specifically aimed at creating a product for making potable water which should have no byproducts that are noxious to living organisms. Such method has the consequent complication of having to remove the disinfectant product by gaseous means.
US-A-2005/0244328 discloses a reactor and a method for the production of chlorine dioxide gas wherein the reactants react in a reaction chamber that operates under elevated pressure and within a specified temperature range.
A problem of such system is constituted by the fact that an excessive pressure is deleterious to the stability of chlorine dioxide.
Another problem is constituted by the safety issues generated by operating at high pressure.